I've just replaced an electric shower with a mixer shower on a gravity fed system and, as I suppose I should have guessed, there isn't enough hot water.

I thought I'd be OK as the bath has mixer taps / shower and works just fine. My new mixer shower is on the same floor as the bath and the hot water cistern. The bottom of the cold water tank in the loft is just short of a metre abover both shower heads. I teed off the pipe that comes out of the top of the cistern and - this is probably where I went wrong - took the pipes up into the loft then back down to the shower. The hot water that goes to the mixer shower on the bath goes down under the floor and back up.

Now that I've tiled and so on, I'm hoping that I can just get away with putting a pump onto the hot water feed in the loft (there's not much spare room in the airing cupboard). Is this possible? If so, are there any recommendations for a pump to do this job? I see that most pumps take both hot and cold water feeds. I suppose it's possible for me to do this, although slightly more work of course.

One day the kitchen ceiling will have to be replaced so at that time I suppose I might be able to re-route the hot water out of the tank, down under the bathroom floor, then back up to the shower but I don't want to have to start that now.

If when taking the pipe feeding the new shower up into the loft you have taken it above the level of water in your cold water storage tank then the only way that hot water could get to the shower is by "syphoning it over that loop. So if you get any at all it will be a very slow flow.

If you've kept the feed pipe below the bottom of the cold tank, I would think that it should work just as well as the one over the bath, provided that the shower heads are the same height. The fact that you've taken it up to the loft and back down shouldn't matter as that loop should always be full. It may be that there is some sort of restriction in the shower head.

Dave, thanks for the reply. It stays below the level of the water tank. Shower heads are more or less the same height although the problem one is perhaps 10cms higher. If I turn off the cold, then switch the shower on and hold the shower head lower down then there is a noticeable increase in the flow.

I started and finished the pipework with copper - up from the tank and down into the mixer - using solder joints, but the run across the floor is the white plastic push-fit type. I cut the copper pipe with one of those cutters with the little wheel that you gradually tighten up and a couple of these cuts did sort of narrow the pipe where I cut it. I also put one of those in-line cut-off valves on. I suppose that must add a bit of 'drag'.

I guess I'm going to have to try adding a pump, so should I pump both hot and cold or just the hot?

Also, because the cold pressure is so good, could cold water be pushing back up into the hot pipe or should the mixer prevent that?

I teed the hot off the pipe that comes out of the top of the hot water cylinder. That pipe turns 90 degrees (ie goes horizontal) straight out of the top of the cylinder. I put the tee piece into that horizontal run. I then went straight up into the loft, along the loft floor then down into the en suite and into the mixer shower. Cold was already there, as I replaced an electric shower. It comes straight out of the cold water tank in the loft and down to the shower.

There's more than enough cold water for the shower. The shower does get some hot water, just not enough. If I take the shower head off the hanger then hold it down near the shower tray - probably 150cm lower than when it's on the hanger, then enough hot comes out.

I no longer have the shower instructions but I'm pretty sure that it did say 0.1 bar. The shower head on its hanger is about 1 metre below the bottom of the cold water tank in the loft. It therefore looks like I need around 2.5m between the shower head and bottom of the cold water tank or 0.25 bar to have an acceptable shower. There's little scope to raise the level of the cold water tank; maybe 50cms max. Anyhow, fitting a pump seems like a much easier, if a little more expensive, way to fix it.

There's a pipe that comes out of the top of the hot water cylinder and immediately bends 90 degrees (ie goes horizontal). I put a tee piece into that horizontal pipe then took it straight up into the loft, across the loft floor then down into my new mixer shower. The cold supply was already there, as I replaced an old electric shower. It just comes out of the main cold water tank in the loft, then straight down.

Cold water pressure on the shower is, of course, great. The shower does get some hot water, just not enough. If I take the shower head off its hanger and let it hang down, then the hot water flow increases to an acceptable level. So the hot water is nearly, but not quite, OK.

I've lost the paperwork that came with the shower but yes, I'm fairly certain it said 0.1 bar was OK.

I could theoretically raise the cold water tank in the loft about 50cm, but I think that fitting a pump would be easier, if it's going to work.

Ah, now we have identified the fault. You can't use low pressure hot and a high pressure cold to supply a mixer shower. Both supplies need to be balanced so the cold should be supplied from a feed taken from the bottom of the cold header tank in the loft.

Having said that, a few models of shower do allow unbalanced feeds by fitting flow restrictors in the feeds. This option is relatively new and I have seen mixed results with the reliability. Did you have bag with two small yellow, green and / or white 1p size discs in?

Fitting a pump just to the hot is not an option and you can't pump mains water.

Download instructions from the manufacturers website and check how the shower can be connected. If you can't find the exact make, look at any make. They are all should be connected the same.

There's no balancing capability on the shower. So yes the cold comes from the header tank, the hot from the hot cylinder. I found this page:

Google "plumbingpages.com/featurepages/SGravity.cfm"

The 'house' seems to be exactly what I have.

Do you reckon that a pump that fed both cold and hot to the mixer would do the job for me? If so, could I put it in the loft, higher than the hot cylinder but lower than the bottom of the cold header tank?

You can put a pump in the loft, but it needs protecting from frost and yet must have ventilation to keep it cool when running which is tricky. Pumps fitted high up can be prone to becoming airlocked so only choose this type of installation as a last resort.

You must consider though, pumps won't balance uneven supplies, just boos the flow of both.

Just a thought, have you tried adjusting the mixer from the manufacturers pre-setting for temperature range?

I've been reading up on this quite a bit now. So I'm going to modify my hot water feed to incorporate an 'anti gravity loop' then go up into the loft. I will also get a cold water feed from the header tank in the loft and attach both to a pump. Then go from the pump to the mixer shower.

According to a Salamander CT50 installation guide I found, I think I need to put an automatic air vent onto both hot and cold on the outlet side of the pump and a non return valve on the outlet side too. I also found a Stuart Turner installation manual (Showermate Eco) but that doesn't say that you have to fit a vent or non return valve.

Do you know either of those pumps and do you reckon they'd be suitable?

Both these makes of pump are regarded as good quality so either should suit your purpose.

When you alter the cold feed make sure it is from its own connection to header tank and not from any existing pipework!

If the run to the shower is reasonably short and all the feeds are below the level of the bottom of the header tank, you should not need a gravity loop or automatic bleed valves.

The only problem you may see is with the relative low water head. Air may be drawn down the expansion pipe into the hot side of the pump. If this occurs fit a Surrey flange to the top of the hot water cylinder.

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